Only sixth known case in United States since 1969, but virus is much less deadly than Ebola

-- Robert Preidt

TUESDAY, May 26, 2015 (HealthDay News) -- A man who returned to the United States after traveling to Liberia in West Africa has died of Lassa fever, federal health officials reported.

Lassa fever is a viral disease that's common in West Africa but rarely seen in the United States. This is only the sixth known case of Lassa fever in a traveler returning to the United States since 1969, according to the U.S. Centers for Disease Control and Prevention.

The last case of Lassa was reported in Minnesota in 2014. There has never been a documented case of person-to-person transmission of Lassa fever in the United States, the CDC added.

The death rate for Lassa is about 1 percent, compared with about a 70 percent death rate for Ebola.

This latest case of Lassa fever involved a man who traveled from Liberia to Morocco and then on to JFK International Airport in New York City on May 17. He did not have any symptoms -- such as diarrhea, vomiting or bleeding -- when he left Liberia or when he arrived in the United States.

By May 18, the man had a sore throat, fever and tiredness, so he went to a hospital in New Jersey. However, when asked about his travel history, the man did not reveal that he had been in Liberia. He was sent home the same day, but returned to the hospital on May 21 when his symptoms worsened, according to the CDC.

The man was transferred to a treatment center equipped to deal with viral hemorrhagic fevers such as Ebola. Tests revealed the man had Lassa fever, but did not have Ebola. The man, who was kept in isolation, died Monday evening, the CDC said Monday.

The CDC is continuing its investigation and working with public health officials to identify people who had contact with the man. Those who had close contact will be monitored for 21 days to see if they develop symptoms of Lassa fever.

Each year in West Africa, there are 100,000 to 300,000 cases of Lassa fever, and about 5,000 deaths from the disease, according to the CDC.

The Lassa virus is carried by rodents and transmitted to people through contact with infected rodents' urine and droppings. In rare cases, it can be transmitted from person-to-person through direct contact with an infected person's blood or bodily fluids, or through sexual contact.

Liberia is one of three West African countries -- the others are Guinea and Sierra Leone -- that were at the epicenter of the 2014 Ebola outbreak, the worst in history.

As of May 22, there have been approximately 15,000 laboratory-confirmed cases of Ebola in those three countries, and 11,125 deaths, according to the World Health Organization.

More information

The U.S. Centers for Disease Control and Prevention has more about Lassa fever.